Before he made Primer for some $7,000, Dallas software-engineer-turned-writer-director-actor-editor Shane Carruth had no idea how to make a movie. Some who see his creation will argue he still doesn't, while others will lavish upon it hearty praise reserved for visionaries who leap from the shadows to the spotlight without any warning. Such has been the reaction to Carruth's time-travel riddle since its debut at the Sundance Film Festival in January, where it snuck into Utah like a cat burglar and skipped out clutching its top honor, the Grand Jury Drama Prize. Even those who adore the movie will caress it with backhanded compliments; "strange, difficult to follow and sometimes pretentious," wrote a colleague as a prelude to a kiss, eventually labeling it "an undeniably impressive debut."

To Carruth's credit, he enjoys downing the flattering praise with a shot of bad news as a chaser. He swears it all makes sense, that one plus one adds up to more than zero if you're at all paying attention, but understands there are just some people for whom his child will be wholly impenetrable. It amuses him to no end, for instance, that as the film's long journey from film-fest obscurity to art-house rollout nears its end, people are starting to whisper that it's actually about ... clones.

It's safe to say that while Primer may be about many things -- chiefly the politics of friendship as it relates to the hazards of time travel, and who hasn't been there? -- it's not about clones. Or perhaps there's a generation of filmgoers that hasn't seen Back to the Future, specifically the scene in which Michael J. Fox returns to the past just in time to glimpse an earlier version of himself reenacting a scene from earlier in the film. Primer takes that moment and expands it even further, to the point where Carruth's entire movie curls in on itself and becomes a loop in time from which there seems to be no escaping, especially if you're bound and gagged and stuck in an attic.

Carruth uses the most mundane settings -- a garage, a suburban living room, a warehouse complex, an airport terminal -- to fashion something unnerving; dark and unknowable things are happening just next door. At the outset we see four guys in ties. Even they don't seem to know just what they're constructing. Finally the quartet whittles down to a duo, Abe (David Sullivan) and Aaron (Carruth), who come to realize that their homemade invention, cobbled together out of spare parts, turns back time, which would delight Cher to no end but comes to confound the audience.

The math is tricky. When Abe and Aaron finally build a larger version of their miniature time machine, which they keep in a warehouse storage facility, they discover they can live 36-hour days, because if they climb in at noon and stay in their holding tanks for six hours, they will come out at 6 a.m. (I think that's right ... hunh.) At first it seems like a good idea: As long as they stay holed up in a motel room -- so no one sees them, including their future selves -- they can make extra money playing the stock market. But eventually, Abe and Aaron turn on each other. One of them, it seems, has violated their agreement not to alter the future by corrupting the past, which is a sci-fi staple -- Star Trek goes to the art house.

Come to think of it, Primer's more like Back to the Future Part II, when Biff makes off with the sports almanac from 2015 containing all the World Series scores from 1950 to 2000. It's a paradox and a puzzle, bereft of laughs but a comedy nonetheless, and absent of tension but thrilling anyway. Things don't always make sense -- especially a party scene during which someone has to go back in time to stop a guy brandishing a shotgun -- but if you give in to the movie, it's not nonsense either. Carruth is an elliptical filmmaker, presenting us with blanks we're either asked or allowed to fill in, depending upon how many times we choose to see the movie and assemble the puzzle pieces. That they go together a dozen different ways only heightens the experience; we're not meant only to experience the movie, but also to interpret it.

There is no question that it will take repeated viewings to understand Primer, to gain even a glimpse of its True Meaning. I've seen it half a dozen times and still don't think I get it, but the pleasure comes not from the deciphering of the puzzle but from the process itself. The whole movie's a buzz -- from the way it looks (jittery, kinetic, but never sloppy) to the way it makes you feel, elated and confused and ready to take another hit of whatever it is Carruth's been smoking. Love it or hate it, you won't be able to leave it alone.

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